1. Field of the Invention
The present invention generally relates to electrophotographic image forming apparatuses, cartridges that can be mounted on main units of the image forming apparatuses, i.e., process cartridges, developing units provided in the form of cartridges, image forming systems, and storage media included in the cartridges.
The electrophotographic image forming apparatuses include, for example, electrophotographic copying machines, electrophotographic printers (e.g., LED printers and laser beam printers), and electrophotographic facsimile machines.
The cartridges that can be mounted on the main units of the electrophotographic apparatuses refer to cartridges including at least one of an electrophotographic photosensitive member, a charging unit for charging an electrophotographic photosensitive member, a developing unit for supplying developer to an electrophotographic photosensitive member, and a cleaning unit for cleaning an electrophotographic photosensitive member. Particularly, a process cartridge refers to a cartridge including an electrophotographic photosensitive member integrated with at least one of a charging unit, a developing unit, and a cleaning unit so that the cartridge can be mounted on and dismounted from a main unit of an electrophotographic image forming apparatus, or a cartridge including an electrophotographic photosensitive member integrated with at least a developing unit so that the cartridge can be mounted on and dismounted from a main unit of an electrophotographic image forming apparatus.
2. Description of the Related Art
In image forming apparatuses that employ electrophotographic image forming processes, the process cartridge system has been used, in which a cartridge including an electrophotographic photosensitive member integrated with process members that act on the electrophotographic photosensitive member can be mounted on and dismounted from a main unit of an image forming apparatus. According to the process cartridge system, maintenance of the apparatus can be performed by a user without calling a service person. This considerably improves convenience of operation. Thus, the process cartridge system is widely used in electrophotographic image forming apparatuses.
Furthermore, according to some proposed techniques, a memory is provided as a storage unit in a process cartridge (hereinafter simply referred to as a cartridge) to store information regarding the cartridge in the memory. For example, according to techniques proposed in Japanese Patent Laid-Open No. 10-221938, the manufacturing lot or the type of cartridge, the type of developer (toner), and so forth are stored in a memory in order to manage the quality of the cartridge.
Furthermore, techniques for achieving stable image quality irrespective of the usage status of a cartridge using information stored in a memory provided in the cartridge have also been proposed. For example, in an image forming apparatus disclosed in U.S. Pat. No. 5,272,503, the number of copies printed (or copied) accumulated as the usage amount of a cartridge in a main unit of the image forming apparatus is recorded in a memory at appropriate timing, and process conditions (image forming conditions) are controlled according to the accumulated value of the number of copies.
Various other techniques for achieving stable image quality have been proposed, for example, in Japanese Patent Laid-Open No. 08-146677, Japanese Patent Laid-Open No. 10-246994, and Japanese Patent Laid-Open No. 11-015214.
In image forming apparatuses disclosed in Japanese Patent Laid-Open No. 08-146677, Japanese Patent Laid-Open No. 10-246994, and Japanese Patent Laid-Open No. 11-015214, a charging bias applied to a charging unit and a developing bias applied to a developing unit are changed in accordance with reduction in the thickness of the photosensitive layer of a photosensitive drum due to use of the cartridge, so that change in image quality due to change in the thickness of the photosensitive layer of the photosensitive drum is reduced.
Furthermore, in order to calculate the degree of usage of a photosensitive drum more precisely, for example, according to techniques disclosed in Japanese Patent No. 3285785, rotation-time information of a photosensitive drum and application-time information of a charging bias applied to a charging unit for charging the photosensitive drum are accumulated and stored in a memory provided in a cartridge, and the amount of usage of the photosensitive drum is calculated precisely using these pieces of information.
Recently, in accordance with the spread of computers, an increasing variety of users has come to use printers, copying machines, facsimile machines, and so forth, and manufacturers now have to produce their products in view of this situation.
Under this situation, as for process cartridges as expendable parts for printers, copying machines, facsimile machines, and so forth, in some cases, different types of process cartridges that can be mounted on the main unit of the same image forming apparatus, having different toner capacities (life spans), are provided. For example, cartridges having larger toner capacities and longer life spans are provided to users who print in large volumes, such as users whose use image forming apparatuses at offices or the like, and cartridges having smaller toner capacities are provided to users who print in small volumes or who prefer inexpensive cartridges, such as personal users of image forming apparatuses.
In the cartridges that have different toner capacities (life spans) and that can be mounted on the main unit of the same image forming apparatus, the configurations of the cartridges are suitably chosen in accordance with their respective toner capacities (life spans). Thus, usually, the thicknesses of the photosensitive layers of photosensitive drums differ between the cartridges as well as the toner capacities. In this case, even when the cartridges are used for the same number of copies or the same period of time, latent-image characteristics (charging characteristics) and development characteristics change differently between the cartridges in relation to the cartridge usage amount. Due to the difference in latent-image characteristics and development characteristics, it has been difficult to achieve stable image quality through correction in all the cartridges having different toner capacities (life spans) with the above-described techniques alone).
For example, using an S cartridge having a shorter life span (a smaller toner capacity) and an L cartridge having a longer life span (a larger toner capacity), process control (setting for switching process conditions in accordance with the drum usage amount herein) suitable for the L cartridge was exercised similarly for the S cartridge irrespective of cartridge type. Comparison between the densities of images obtained with the S cartridge and the L cartridge demonstrated a density difference of 0.05 to 0.1 at halftone densities with a print ratio of 25%, as shown in FIG. 15. That is, images of different qualities were obtained due to the difference in cartridge type between the S cartridge and the L cartridge used in the same image forming apparatus.
This indicates that even when the same image is printed, a density difference could occur due to difference between the types of cartridges used.